While other super PACs pour millions of dollars into attack and issue ads, Credo Mobile's super PAC is eschewing the media war in favor of retail campaigning.

It's investing in field offices and a staff of 30 full-time employees who manage thousands of volunteers - a strategy that could be particularly effective in the tight races where unaffiliated and party committees as well as social welfare nonprofits are blanketing the airwaves.

Voters in the Sacramento, Calif., suburbs, for example, are in the cross hairs of a relentless political media barrage thanks to tight California State Senate and Assembly races, a series of contentious ballot measures and two highly competitive Congressional contests, including four-term Republican Rep. Dan Lungren's re-election bid. Lungren, who previously served five terms, is one of Credo's targets.

"We are reaching a real saturation point on television, and for any outside group to understand that and invest in ground game is probably a wise move," said Dave Gilliard, a Republican consultant who is advising the re-election campaign of Rep. Jeff Denham (R-Calif.) in the neighboring 10th district. "The problem with this group is that their public messaging is very far to the left."

Lungren is locked in a tight race with his 2010 opponent, Democratic physician Ami Bera, in California's redrawn 7th district. Roll Call rates the race as a Tossup.

Credo's strategy and its anti-tea-party message is well-suited for the new map, which loops in more Democratic voters while cutting out Republicans in the rural eastern part of the district, with easy-to-walk suburbs and a high concentration of what Gilliard described as "casual voters."

Jeff Wyly, a spokesman for Lungren's campaign, dismissed Credo's activities as irrelevant in a district with an almost equal number of registered Democrats and Republicans.

"They are organizing their base liberals," he said. They are not reaching out to independents."

But he acknowledged that is exactly what Bera needs. "If you look at the primary results, Bera definitely has a base problem, a Democrat problem," he said.

The group is focusing on a list of 33,000 people who voted in 2008 but not in 2010 and "are modeled as 65 percent or better to vote Democratic" this year, a spokeswoman said in an email.

The National Republican Congressional Committee and other GOP-aligned outside groups, including American Action Network, recently launched another round of advertising in defense of several of the lawmakers whom Credo has dubbed the "Tea Party Ten," including Reps. Sean Duffy (Wis.), Steve King (Iowa), Chip Cravaack (Minn.) and Jim Renacci in Ohio's newly drawn 16th district.

"We hope that there's a tipping point at which people will become disgusted by advertising," said Becky Bond, the president of Credo SuperPAC and the company's political director.

The group is taking advantage of the 2010 Supreme Court ruling that made it legal for corporations to make unlimited political donations - through PACS or autonomously - so long as they operate independently from candidates.

The phone company's customers and corporate treasury had donated more than $2 million to the PAC as of Aug. 30, according to reports filed Sept. 20 with the Federal Election Commission.

Of every customer's monthly charges, 1 percent goes to liberal nonprofit groups. The phone bill itself doubles as a newsletter from the progressive world.

Earlier this year, the phone company started asking its customers to overpay their bills in support of its new super PAC. Those funds are then transferred to the super PAC as a corporate donation, one that would have been prohibited before the Supreme Court ruling in Citizens United v. Federal Election Commission.

So far, the group has invested about $165,000 in each of the 10 districts - a pittance in comparison to what other outside groups have spent. In Minnesota's 8th district, where Cravaack is facing former Democratic Rep. Rick Nolan (D), outside groups have spent more than $1.65 million on independent expenditures, making it one of the most expensive House races this cycle, according to the nonpartisan Center for Responsive Politics.

Ben Golnik, a spokesman for the Cravaack campaign said the grass-roots army that helped his candidate oust 18-term Rep. Jim Oberstar in 2010 "vastly outnumbers any outside group that may come in for a short period of time."

A spokeswoman for the PAC said it has almost 1,300 volunteers ready to pound the pavement in Cravaack's district.

The super PAC, which concentrated on protests and building its volunteer ranks throughout the summer, will focus almost exclusively on voter contact until Election Day, the spokeswoman said.

In Lungren's district, the group has signed up 972 volunteers who have made more than 45,000 calls and knocked on 2,600 doors, she said.

"Any group in a Congressional district who has 950 volunteers should take over the world," said Matt Rexroad, a Republican consultant and redistricting expert with Meridian Pacific in Sacramento. "And I don't see anyone taking over the world."

Still, Lungren's campaign is on notice.

In late August, Credo sent dozens of activists to demonstrate at three town hall meetings that Lungren hosted. Before the third, Lungren's chief of staff, Peter Tateishi, asked the local Tea Party Patriots chapter for support.

"The past two town halls have been hijacked by protesters with the group Credo PAC," wrote Tateishi, who is running for California State Assembly in November. "The Congressman was hoping we might be able to get a number of members to his last town hall to counter the protesters and show that the Tea Party is alive and well and not going to let any group bully them around."